Maintenance of conductivity in electrical systems



April 21, 1953 R. SHERMAN 2,636,131

MAINTENANCE OF CONDUCTIVI TY IN ELECTRICAL SYSTEMS Original Filed Dec.31, 1946 "if /4/0 06 M08 M20: 7 K 4 I M03 cj i WV. I i J v v I /4//3/4/59 :0 /402 /4/7 1 INVENTOR.

" EAL/w SHLPMAN ATTORNEY Patented Apr. 21, 1953 MAINTENANCE OFCONDUCTIVITY IN ELECTRICAL SYSTEMS Ralph Sherman, Warren, Ohio Originalapplication December 31, 1946, Serial N 0.

719,368. Divided and this application November l, 1950, Serial No.193,406

9 Claims. (Cl. 307-13) This application is a division of my copendingapplication, Serial No. 719,368, filed December 31, 1946, on whichPatent No. 2,528,558 was granted November 7, 1950.

This invention relates to the maintenance of conditions of goodconductivity in electric systerns, It is concerned more particularlywith the protection of low voltage and current circuits, such asmeasuring circuits, signalling circuits and the like containin a numberof contacting conductive parts (contacts).

It is a well known fact that electrical systems of this kind arefrequently endangered by an appreciable deterioration of contactbetweencontacting conductive parts, which may be caused by the.formation of thin oxide layers and other insulating layers at pointsexposed to the action of heat, dust, oxidizing gases or the like.

It is one of the objects of this invention to maintain, in spite of suchdisturbances, a fair degree of conductivity at such contacts whereby toprevent temporary or extended interruption of the circuit.

It is thus, an object of the invention to obtain a high degree ofreliability and continuity of service in electric systems and in devicesfor electric systems such as protective circuits and measuring circuits,including those circuits in which relatively low voltages act, or inwhich even very slight deterioration of contacts or minute deviation incontact resistance may have disadvantageous. or even disastrous results.A further object. of the invention is to provide circuit restorationmeans which are not only highly reliable and have assured continuity offunctioning, but which are. also inexpensive and of the. utmostsimplicity.

Other and further objects, features and advantages of the invention willbecome apparent as the description proceeds.

In my copending application, Serial No. 719,367, filed December 31,1946, I have disclosed and claimed an arrangement for testing andeventual-1y improving the conditions of conductivity of electric systemscontaining contacts which comprises sending from time to time throughthe contacts current impulses of a voltage exceeding the voltagenormally impressed on the contacts to such an extent that anyinsuificiently conductive layer which may have formed between thecontacting parts, is punctured and full conduc- As explained in myaforesaid parent application, Serial No. 719,368, good conditions ofconductivity can be maintained also, without any part of the circuitbeing required to be cut out beforehand, by providing means for guidingthe restoring current in such manner as to allow it to act on thecontacts without aifecting the instrument or instruments. In consequenceof this arrangement the restoring current can be fed permanently to thecircuit to be protected. This current may be furnishedby a separatesource, whose E. M. F. amounts to a multiple, frequently a thousandfoldof that which normally arises as drop of potential in that section ofthe circuit. This materially higher E. M. F. causes any considerableinsulating layer formed between two contacting parts to be punctured atonce, or a degree of conductivity to be restored which offers noexcessive resistance to the passage of very small measuring currents.

Restoring may already take place with a current amounting to a fractionof one ampere. However, under certain conditions the maximum amperage tobe supplied to contacts of low amperage measuring circuits must notexceed a few amperes, as otherwise the to be restored contacts mightburn out. Thus, according to the present invention, the restoringcurrent may be fed to the system to be protected permanently and withoutany interruption and any deteriorated contact will be improved and fullconductivity restored by it automatically, While the main circuit istraversed by its working current.

The guiding or blocking mean which deflect or block the auxiliaryrestoring current from the section containing sensitive instruments ordevices, allow the working current, such as the measuring current in ameasuring system, to pass through such section without any hindrance.These guiding or blocking means enable such a current intensity orvoltage to arise in any section of the system as may be required for therestoration of the endangered contact, by concentrating the eiiect ofthe restoring current on that part of the system which contains thecontact or contacts which may require restoration.

The intensity of voltage of the restoring current may be controlled byconventional measuring instruments (ammeters and voltmeters) which willalso indicate any deterioration of conductivity at the contacts withinany section of the system.

In the drawings aiiixed to this specification and forming part thereof,a number of embodiments of the invention are illustrateddiagrammatically by way of example.

In the drawings:

Fig. 1 is a diagram of an A. C. measuring system protected by a D. C.restoring arrangement.

Fig. 2 shows the protection of electric contacts by mechanical means,and

Fig. 3 illustrates another arrangement in which the mechanical partsslide on the contact surface.

Referring to the drawings and first to Fig. 1, only a voltmeter 562 isshown here as the measuring instrument in the electric system, but itshould be understood that it stands here for any type of measuring orindicating instrument or device adapted for use in such a system. Thesystem further comprises an electrode holder 2 and electrode 3 of anelectric arc furnace containing a body of molten metal. The workingcurrent or load current is fed to the holder 2 through the wire Iconnected to the point 4. The measuring instrument 562 is provided toindicate any variations of the drop of potential between the holder 2and its electrode 3. It is connected to the holder at 6, to theelectrode at 1. These two contacts are subject to the action of theheat, the dust and the gases issuing from the body of metal 5 in thefurnace and the conductivity at these points is bound to deteriorateunder this action, whereby the indication of changes of the drop ofpotential by the voltmeter would be rendered faulty.

Restoration of conductivity of these contacts is effected whenever anymaterial deterioration has taken place, by an additional current fed tothe system from a current source 556 and flowing through the connectionpoints 5 and/or 1, this additional current having an E. M. F. andintensity such that it will puncture the insulating layer formed betweenthe contacting parts.

In order that this restoration can take place automatically duringoperation of the system and without any danger to the voltmeter or thelike, I provide guiding means which force the restoration current toflow through a predetermined path which avoids the measuring instrument.1 In the present case, where the current source (battery 566) furnishesdirect current, the the rectifier (valve) 564 acts as guiding orblocking means for diverting restoration current. from the measuring ordetecting instrument or other auxiliary device or circuit responsive toelectrical conditions at the points 5 and 1. In the circuit comprisingthe measuring instrument 552 alternating current flows from theconnection 5 at the electrode holder 2 through the wires 8 and 56!,voltmeter 5E2, wire 563, rectifier 554, wires 565 and 9 to theconnecting point 1 on the electrode 3'. The valve 564 as such wouldallow only onehalf Wave of the drop of potential to pass through.However, since it is not the absolute value of this drop of potential,but its changes, that is of interest here, the passage of one-half of awave is all that is required.

At the same time current flows from the positive pole of the source 566of direct current through the regulating resistance 551, wires 568 and569, ammeter 510, choke coil 513, Wire 51 3, connection 519, wire 9,connection 1, electrode 3, electrode holder 2, connection 6 of themeasuring circuit, wire 8, connection 589, wire 515, and wire 511, backto the negative pole of the current source 565.

.The current, being positive at the connection 519, is not capable ofpassing through the rectifier 564, as this latter is arranged in thecircuit, but is forced to take the way through wire 9 and the measuringconnection 1 and B. On applying suificient amperage and voltage, thecurrent will puncture any insulating layer which may have formed at thepoints 5 or 1, and will thus restore conductivity automatically, whilethe measuring system is being traversed by its (alternating) workingcurrent. The amperage is regulated by means of the regulating resistance551. The E. M. F. of the current source 556 may also be maderegulatable, if desired.

While the amperage passing through from the protective device isindicated by ammeter 519, the voltage is indicated by voltmeter 518.These two instruments allow of watching the degree of conductivity atthe contacts 5 and 1. This is facilitated by the use of a current of anintensity which may amount to hundred times the intensity of themeasuring current in the system. If for some reason it should bedesirable to obtain exact data regarding the degree of deterioration ofconductivity at the contacts, the E. M. F. from the source of restoringcurrent should be chosen as low as not to enable the insulating layer tobe punctured, whereupon it should be raised gradually until puncturingoccurs. The voltage required to do it can thus be ascertained easily.Moreover, the successful functioning of the circuit restoration means isvery easily checked visually by reliable, simple instruments such as theammeter 519 and the voltmeter 518, either or both of which might alsotake the form of automatically operating indicators or alarm devices ifautomatic check up on the functioning of the circuit restoration isdesired.

As shown, the source of restoration current 559 is a simple batteryreliable in functioning,

and the electromotive force of which depends in no manner upon themaintenance of good con- Moreover, if some tacts in any of its elements.contact deterioration should take place such as in the connections tothe battery, in the con nections in the rheostat 561 or in the slidingtap, or in the connections to the ammeter 519, to the choke coil 513, orin the connections to the measuring circuit at 519 and 58, automaticrestoration of circuit conductivity at these points is automaticallyassured by the same means as circuit conductivity is restored, ifnecessary, throughout the auxiliary circuit to be supervised or to beprotected such as at the contacting con ne'ction terminals 6 and 1.

It is quite evident that the circuit restoration means illustrated isinexpensive and very simple.

For the reasons indicated it has a high degree of reliability, not onlyin the functioning but in the assurance of the continuance of the supplycurrent. Variations in the circuit contacts in the circuit to besupervised have no effect on the output or electromotive force of thecurrent source 565. The degree of restoration which is provided such asin the contact at the terminals '6 and 1, for example, is in proportionto the need therefor. This happens because the greater the contactdeterioration, the greater its resistance and the greater the voltagedrop therein, so therefore, the greater the restorative effect of therestorer current from the source 566. Good contacts are thus assured inthe auxiliary or measuring circuit including the connections of theconductors 8 and 9 and of the voltmeter 562.

As shown in Fig. l, the arrangement is employed for supervising contactssuch as might be employed if desired for connecting leads 8 and 9 to theelectrodes 2 and 3. These contacts may be either movable or temporarycontacts or they may be so called permanent or fixed contacts: Moreover,my circuit restoration system functions effectively even though thecontact resistance such at as the terminals 6 and I may be very small incomparison with internal battery resistance, current limiting resistancesuch as in the rheostat 567, the ohmic component of the impedance of thechoke coil 513, etc.

The choke coil 573 prevents the indications of the main instrument 552from being influenced by opposing a. high resistance to the alternatingcurrent, i. e. to the drop of potential between the electrode and itsholder, while to the direct current from the protective device it offersonly a comparatively low ohmic resistance. Therefore the; protectiondevice may be inserted any lengthof time without influencing themeasurements of the instrument 552.

Any appreciable partial deterioration of any contact in the respectivesection of the measuring circuit, and more especially of the contactsand I, will be instantly removed. At the same time the indicatingdevices in the restoring circuit continually indicate the actualcondition of the respective part of the circuit.

If these indicating devices are combined with suitable signalling means,a signal will become perceptible, for instance, visible or audibleautomatically as soon as one of the measuring contacts has suffereddeterioration to such an ex- 0 tent that it could not be restored.

The rectifier 504, as Was mentioned above, allows the passage of only ahalf wave of the alternating voltage to be measured. II" it should bedesired to afford passage for the entire Wave.

the rectifier might be replaced by a condenser, which blocks the directcurrent from the restoring circuit as efiectively as the rectifier.

If the working current amperage passing between the electrode 2 and itsholder is very high, while the inner resistance between these parts isvery low, as is the case with electric furnaces, the choke coil 513 maybe dispensed with and the protective device may still be insertedpermanently in the circuit without influencing the measuring instrument552.. But also if the inner resistance is high, the choke coil may bedispensed with, it the protective device is actuated only for a shortperiod of time, since then the instrument 562 will also be influenced'only during a short period of time. One may also dispense with aregulation of the source of direct current 560.

The voltmeter and ammeter of the restoration circuit may be replaced byan incandescent lamp or any other suitable device which, if connected inseries with the current source, may serve directly as a limitationresistance and as a crude kind of indicating device for the passage ofcurrent and for its amperage. Another lamp or other parallel connectedvoltage-responsive device may crudely indicate the potential.

The above described restoring device may be used also if the workingcurrent. does not flow in the network.

Fig. 2 illustrates the protection of the contacts with the aid of partlymechanical means. For the sake of clearness mechanical protection ofcontacts is shown only with reference to one contact point, between theelectrode I403 and contact spindle I404, but obviously such protectionmight also be provided at all other contact points. I40I is a currentsupply to the electrode holder I402 from which the current flows throughthe electrode I403 and the body I405. of

molten metal. The drop: of potential between the electrode holder andthe electrode is measured with the aid of a wire I408 connected to theelectrode holder I402 at I42I and leading to the voltmeter I422. Theother measuring wire is here connected to the electrode I403 by means ofa screw spindle I404-with a point I402 0. The spindle is supported intwo bearings I400 and Hill, with insulating material IMO and I4I2,respectively, holding the bearings in place. At the spindle and oppositethe point I420, the measuring wire I4I3 is fixed by soldering orWelding, the other pole of the instrument I422. I420 of the spindle I404material and smoke gases. Nevertheless, under the conditions existing inan electric furnace the point will after some time be subject tooxidation. During operation of the furnace dust settles on the electrodeand, therefore, the contact between the point I420 and the electrode maybe poor from the beginning or may deteriorate considerably duringoperation.

In order to counteract this, the spindle I404 is forced withconsiderable pressure by a spring I406, acting on the collar I401against the bearing I400, and its point I420 is thus forced against theelectrode I403. A motor I410 drives by means of a spindle I4I8 a gearI4I1 meshing with a gear I M6 on spindle I404. The motor is controlledby a switching device (not shown) of well known construction, forinstance, in combination with a worm gear which causes it to make shortturns alternately to the right and to the left whereby the spindle I404is constantly reversed also. Owing to the combined axial and alternatingcircumferential movements of the spindle, sliding friction is createdbetween the point i420 and the electrode. This sliding friction keepsthe contacting surfaces clean by loosening any oxide layers which mayform. The pressure exerted by the spring could be such that the pointI420 gradually enters the electrode material, whereby a good contact isensured.

The wire I4I3 may also be connected to the motor spindle by means of acollector brush sliding on a collecting ring (not shown) mounted on. andconnected to, the spindle I404.

The spring I405 might be arranged in some other place and may beassisted, or replaced, by any other pressure-producing medium, includingfor instance a solenoid. The pressure exerted on the contact point maybe permanent or intermittent. This device can be used not only withcarbon electrodes, but also with conductive bodies of some othermaterial, and more especially with metal.

In any case provision must be made for a relative shifting underpressure of the contacting surfaces occurring permanently or atintervals.

The described moving of a contacting part may, of course, be eiiected byany suitable means.

3 illustrates. the protection of contact with the aid of mechanicalmeans producing a sliding movement on the contact surfaces.

Here I50I indicates the current feed to the electrode holder I502, theelectrode I503 and the body I 505 of a molten metal.

The drop of potential between the holder and the electrode is indicatedby the voltmeter I520 which is connected to the holder I 502 by a wireI504. The other terminal of the voltmeter is connected to, the electrodeI503 by wire I501.

The point is preferably made of a this wire leading through wire. I 414to which can withstand the action of heat,

pliable wire I506 and contact brush I508, to which wire I505 may bewelded. This brush is forced against the electrode by a spring II0acting on the brush through an insulating piece I503. Since, in spite ofthe pressure exerted on the brush, oxidation of the contact surface maybe caused by the heat or the action of gases, I provide forreciprocatory sliding movement of the brush by means of a drivingmechanism comprising the worm gear I5I8, I5II, an eccentric I522 on thegear, a rod I5I6, link bolt I5I5 and link I5II extending through a guideI 5I2 fixed at I5I by means of an insulating piece I5I3. The brushreciprocated by this mechanism, being acted upon by the spring I5IEl,creates sliding friction on the surface of the electrode I553 wherebyany oxide layer and dust deposited on this surface is removed and goodconductivity secured.

Instead of a metal brush, a carbon brush may be used, more especiallywhen the conductor iS made of metal, whereby any appreciable wear on thecontact surface is avoided. G1" course, the carbon brush, when moving,may follow simultaneously any other path, for instance, a circular orelliptic one.

Also in Fig. 3, for the sake of clearness, mechanical means forprotecting contacts are shown only at one point of contact. In caseswhere the measuring contact is exposed to particularly strong injuriousaction, both kinds of restoring devices, mechanical and electrical, maybe combined. If in certain cases it should appear desirable to ascertainwhether a material deterioration has occurred, the same restoringarrangement can be applied, however the restoration voltage should thenbe so low at the start that a puncturing to restore conductivity cannotbe obtained. The voltage is then raised gradually and by watching boththe voltage and the amperage one can find out whether an insulatinglayer has been punctured. The value of the voltage required will allowthe degree of deterioration to be ascertained.

In order to facilitate reading the instruments, they may be providedwith a plurality of measuring ranges and/ or amplifiers may be used. Therestoring device may also be combined with a signalling device whichwill give a warning in case the deterioration has proceeded to a pointWhere no improvement is possible any more. Then the condition of thecontacts can be watched constantly. The restoring eifect is obtainedautomatically while the measuring system is in full operation.

In Figs. 2 and 3, the combined res-torer effect may be obtained,including that of the mechanical action of rotating or sliding contactand the electrical action of a source of contact maintaining voltagesuch as illustrated in Fig. l or in the other figures of my parentapplication, Serial No. 719,368, or that of intermittent or soleelectrical impulse effect such as described more particularly in mycopending application, Serial No. 719,367, filed December 31, 1946.Although a specific type of mechanically acting contact conductivitymaintaining arrangement has been disclosed in Figs. 2 and 3, it will beunderstood that the invention is not limited thereto, and does notexclude the use of the mechanical action of sound waves or supersonicwaves in the maintenance of contact conductivity nor does it exclude useof artificially or naturally produced electromagnetic fields, singly orin combination with other forms of conductivity maintenance described inmy aforesaid parent application, Serial No. 719,368 and the copendingapplication, Serial No. 719,367.

Whenever no supervision of the contacts is required, the restoringdevice can be simplified materially. For instance, the means forregulating the voltage may be dispensed with and the measuringinstruments may be much simpler or may even be replaced by incandescentbulbs.

While in the foregoing only combinations of the restoring device withmeasuring systems of various kinds has been described, it will beobvious that it will be of equal use in combination with any other kindof electrical system operating with low amperages and voltages, forinstance, signalling or checking systems. Also rotary contacts may besupervised and kept in a high state of conductivity by its application.

When the deterioration of the conductivity in contacts exceeds a certainlimit, the restoring current may give rise to very high voltages whichmight injure the guiding or blocking devices. This may be prevented bythe use of conventional devices for overvoltage protection.

The rectifiers, choke coils, etc., serving as guiding or blocking meansmay, of course, be replaced by any other devices capable of allowing therestoring current to pass through the section to be protected of thesystem, but counteracting its injurious action on other sections. Evenelectronic valves may serve the purpose if they are so arranged as toprotect the measuring instrument against the action of excess voltage.This may be used, in a well known manner, for creat-' ing a shortcircuit path and/or abolishing the excess voltage created by therestoring device.

It may be well to point out also the utility of a restoring deviceaccording to the invention, if used in connection with measuring methodsserving to supervise rivet connections, welding joints and screwconnections during or after manufacture. Such methods operate withseparate current which passes through the contacting paths and indicatechanges of the voltage drop. They were hitherto not adapted for use astesting methods during operation of a machine or engine because, if thecontact in the measuring circuit should deteriorate or open upaltogether, the entire measuring system would cease to act. Here also arestoring device will enable the correct functioning of such a system tobe maintained permanently. Important joints in steam engines,

diesel engines, airplane structures and the like; may thus be supervisedreliably through an indefinite period of time.

Various changes may be made in the structural combinations of means andin the operation of the devices hereabove described without departingfrom the spirit of the invention or sacrificing the advantages thereof.

What is claimed is: V

1. In combination with a detecting instrument having leads adapted to beconnected to points in a system of predetermined voltage, for responseto electrical conditions at such points, such leads and connectionsincluding contacts subject to formation of layers of low-conductivityand in capable of being broken down by voltages of said predeterminedvalue, mechanism for producing relative movement between one of thecontacts and the member against which it lies.

2. In an electrical current conducting system having connectionsincluding contacts subject to formation of layers of low conductivityand incapable of being broken down by voltages nor- .mally present inthe system, mechanism for pro-,

ducing relative movement between one of the contacts and the memberagainst which it lies.

3. Apparatus as set forth in claim 2 in which the motion producingmechanism includes a drive shaft for rotating the movable contact.

4. Mechanism as in claim 3 wherein the contact moving mechanism includesa reciprocating device for rubbing the contact along the member againstwhich it lies.

5. Mechanism as in claim 2 whereas the relatively movable contacts aresubjected to the action of sound waves and the motion producingmechanism comprises a sound wave generator.

6. Mechanism as in claim 2 whereas the relatively movable contacts aresubjected to the action of supersonic waves and the motion producingmechanism comprises a supersonic wave generator.

7. Apparatus as in claim 2 wherein the contacts having layers of lowconductivity are subjected to the action of electromagnetic waves forbreaking down such layers.

8. Apparatus as in claim 2 wherein the conductivity maintaining actionof relatively movable contacting members is utilized in combination witha conductivity maintaining effect of one of the group of effectsproduced by single voltage impulses, intermittent voltage impulses,permanently applied conductivity-maintaining voltage, andelectromagnetic waves, and the rela tive mechanical motion is producedby one of the group of forms of mechanical energy consisting ofsupersonic waves, audible sound Waves. rotatively driven mechanism, andreciprocating mechanism.

9. In an electrical current conducting system having connectionsincluding contacts subject to formation of layers of low conductivityand being incapable of being broken down by voltages present in thesystem, a source of electromagnetic waves continuously functioning andmechanism for subjecting the system to the action of suchelectromagnetic waves.

RALPH SHERMAN.

Number Name Date Hornickel Dec. 19, 1939

